Why Measles Causes TB Reactivation in Children
Measles virus causes profound and prolonged suppression of cell-mediated immunity, which is the primary defense mechanism against tuberculosis, leading to reactivation of latent TB infection in children.
Mechanism of Immunosuppression
Measles induces temporary but severe immunosuppression that specifically impairs the cellular immune responses critical for controlling M. tuberculosis. This immunosuppressive effect manifests as:
- Complete anergy during acute measles: All tuberculin-positive children become anergic (unable to mount a delayed-type hypersensitivity response) during the acute phase of measles infection 1
- Prolonged immune dysfunction: The suppression of tuberculin reactivity persists for 2-7 weeks after the measles rash appears, with children who develop complications remaining unreactive significantly longer (mean 4 weeks) compared to uncomplicated cases (mean 2.3 weeks) 1
Why This Matters for TB Control
The cell-mediated immune response, particularly CD4 and CD8 T-cells secreting interferon-gamma, is essential for maintaining M. tuberculosis in its dormant state within granulomas 2. When measles disrupts this immune surveillance:
- Loss of granuloma integrity: The immunosuppression allows dormant bacilli to metabolize and multiply at higher rates, reaching numbers sufficient to cause clinically manifest disease 2
- Increased risk in young children: Children, especially those under 5 years, already have the highest risk of progression from latent infection to active TB disease, and measles compounds this vulnerability 2
Clinical Implications
Children with known or suspected latent TB infection who develop measles require heightened surveillance for signs of TB reactivation, including:
- Persistent fever beyond the expected measles course
- Progressive respiratory symptoms (cough, dyspnea)
- Failure to thrive or weight loss
- Signs of disseminated disease (meningitis, miliary TB) 2, 3
Common Pitfall
The major diagnostic challenge is that tuberculin skin testing becomes unreliable during and after measles due to the induced anergy 1. This means:
- A negative tuberculin test during or shortly after measles does not exclude TB infection or disease
- Clinical suspicion must guide evaluation rather than relying on skin test results
- Testing should be deferred until immune function recovers (typically 4-8 weeks post-rash)
Immunosuppressive disorders are recognized as aggravating risk factors for TB progression 2, and measles represents a temporary but clinically significant immunosuppressive state that creates a window of vulnerability for TB reactivation in children with latent infection.